Top metal contact for vertical transistor structures

ABSTRACT

A vertical transistor includes a source layer arranged on a substrate; a channel extending vertically from the source layer; a drain arranged on a distal end of the channel that opposes the source layer, the drain including an epitaxial growth; and a drain contact wrapped around exposed areas of the drain and filling a cavity having a liner layer disposed sidewalls of the drain contact.

BACKGROUND

The present invention relates to complementary metal oxide semiconductor (CMOS) technology, and more specifically, to vertical transistor semiconductor devices.

CMOS is used for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static random access memory (RAM), and other digital logic circuits. CMOS designs may use complementary and symmetrical pairs of p-type and n-type metal oxide semiconductor field effect transistors (MOSFETs) for logic functions.

The MOSFET is a transistor used for switching electronic signals. The MOSFET has a source, a drain, and a metal oxide gate electrode. The metal gate is electrically insulated from the main semiconductor n-channel or p-channel by a thin layer of insulating material, for example, silicon dioxide or high dielectric constant (high-k) dielectrics, which makes the input resistance of the MOSFET relatively high. The gate voltage controls whether the path from drain to source is an open circuit (“off”) or a resistive path (“on”).

As MOSFETs are scaled to smaller dimensions, various designs and techniques are employed to improve device performance. Vertical transistors, in which source/drain regions are arranged on opposing ends of a vertical channel region, are attractive candidates for scaling to smaller dimensions. Vertical transistors may provide higher density scaling and allow for relaxed gate lengths to better control device electrostatics, without sacrificing the gate contact pitch size.

SUMMARY

According to an embodiment, a method of forming a drain contact of a vertical transistor includes forming a channel that extends vertically from a source and through a trench within a sacrificial gate material layer and a gate spacer layer, the gate spacer layer arranged on the sacrificial gate material layer; recessing the channel and depositing a dielectric material to form a dielectric cap on a distal end of the channel and over the gate spacer layer; performing an epitaxial growth process to form an epitaxial growth on a distal end of the channel in a region between the dielectric cap and the gate spacer layer, the epitaxial growth forming a drain; forming spacers around the drain that extend from the gate spacer layer and are arranged on sidewalls of the dielectric cap; depositing a liner layer on sidewalls of the spacers; removing the spacers and the dielectric cap within the liner layer to form an open cavity within the liner layer and to expose the drain; and filling the open cavity with a metal to form the drain contact, the drain contact extending from the gate spacer layer and surrounding exposed areas of the drain.

According to another embodiment, a method of forming a drain contact of a vertical transistor includes forming a channel that extends vertically from a source and through a trench within a sacrificial gate material layer and a gate spacer layer, the gate spacer layer arranged on the sacrificial gate material layer; recessing the channel and depositing a dielectric material to form a dielectric cap on a distal end of the channel and over the gate spacer layer; performing an epitaxial growth process to form an epitaxial growth on a distal end of the channel in a region between the dielectric cap and the gate spacer layer, the epitaxial growth forming a drain; forming spacers around the drain that extend from the gate spacer layer and are arranged on sidewalls of the dielectric cap; replacing the sacrificial gate material layer with a metal gate that is arranged on sidewalls of the channel between the source and the drain; depositing a liner layer on sidewalls of the spacers and the gate; removing the spacers and the dielectric cap within the liner layer to form an open cavity within the liner layer and to expose the drain; and filling the open cavity with a metal to form the drain contact, the drain contact extending from the gate spacer layer and surrounding exposed areas of the drain.

Yet, according to another embodiment, a vertical transistor includes a source layer arranged on a substrate; a channel extending vertically from the source layer; a drain arranged on a distal end of the channel that opposes the source layer, the drain including an epitaxial growth; and a drain contact wrapped around exposed areas of the drain and filling a cavity having a liner layer disposed sidewalls of the drain contact.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIGS. 1A-22B illustrate exemplary methods of making a semiconductor device according to embodiments, in which:

FIGS. 1A and 1B are a cross-sectional side view and a top view, respectively, of a dummy gate and dielectric capping layer arranged on a substrate;

FIGS. 2A and 2B are a cross-sectional side view and a top view, respectively, after forming a trench through the dielectric capping layer and the dummy gate to expose the first spacer;

FIGS. 3A and 3B are a cross-sectional side view and a top view, respectively, after etching through the first spacer to expose the doped source;

FIGS. 4A and 4B are a cross-sectional side view and a top view, respectively, after oxidizing a portion of the dummy gate sidewall;

FIGS. 5A and 5B are a cross-sectional side view and a top view, respectively, after growing an epitaxial layer within the trench to from a channel region;

FIGS. 6A and 6B are a cross-sectional side view and a top view, respectively, after planarizing the epitaxial layer;

FIGS. 7A and 7B are a cross-sectional side view and a top view, respectively, after partially recessing the epitaxial layer, filling with a dielectric material, and planarizing;

FIGS. 8A and 8B are a cross-sectional side view and a top view, respectively, after removing the dielectric capping layer and forming an epitaxial growth on the channel region to form a drain;

FIGS. 9A and 9B are a cross-sectional side view and a top view, respectively, after depositing a spacer on the drain;

FIGS. 10A and 10B are a cross-sectional side view and a top view, respectively, after removing a portion of the second spacer and dummy gate;

FIGS. 11A and 11B are a cross-sectional side view and a top view, respectively, after removing remaining portions of the dummy gate;

FIGS. 12A and 12B are a cross-sectional side view and a top view, respectively, after removing the dummy gate oxide layer and depositing a dielectric material and a work function metal;

FIGS. 13A and 13B are a cross-sectional side view and a top view, respectively, after filling with a metal gate material and planarizing the metal gate material;

FIGS. 14A and 14B are a cross-sectional side view and a top view, respectively, after partially recessing the metal gate material;

FIGS. 15A and 15B are a cross-sectional side view and a top view, respectively, after etching the dielectric material and the work function metal;

FIGS. 16A and 16B are a cross-sectional side view and a top view, respectively, after performing gate lithography and etching to form the gate;

FIGS. 17A and 17B are a cross-sectional side view and a top view, respectively, after depositing a liner layer on the gate and the spacers around the drain;

FIGS. 18A and 18B are a cross-sectional side view and a top view, respectively, after depositing an inter-layer dielectric (ILD) on the liner layer and planarizing;

FIGS. 19A and 19B are a cross-sectional side view and a top view, respectively, after forming source contacts;

FIGS. 20A and 20B are a cross-sectional side view and a top view, respectively, after forming gate contacts;

FIGS. 21A and 21B are a cross-sectional side view and a top view, respectively, after removing the dielectric material and spacers around the drain; and

FIGS. 22A and 22B are a cross-sectional side view and a top view, respectively, after depositing a metal on the drain to form drain contacts.

DETAILED DESCRIPTION

Although vertical transistors may be used for smaller device scaling, one challenge that may arise in vertical transistors is contact resistance. In particular, contact resistance at the top contact electrode (drain contact) may too high, which can reduce device performance.

Accordingly, various embodiments provide vertical transistor devices and methods of making vertical transistor devices with reduced contact resistance at the top contact (drain contact). In embodiments, an all-around metal top contact (drain contact) is formed (see FIGS. 22A and 22B). A liner layer is depositing on sidewalls of the spacer surrounding the drain (see FIGS. 17A and 17B), which allows for the spacer surrounding the drain to then be selectively etched (see FIGS. 21A and 21B) and replaced with a drain contact metal. The contact metal surrounds the drain, instead of only contacting a surface of the drain, which reduces resistance.

It will be understood that when an element, such as a layer, region, or substrate is referred to as being “on” or “over” another element, it can be directly on the other element or intervening elements may also be present. In contrast, when an element is referred to as being “directly on” or “directly over” another element, there are no intervening elements present, and the element is in contact with another element.

Turning now to the Figures, FIGS. 1A-22B illustrate exemplary methods of making vertical transistor devices according to embodiments. FIGS. 1A and 1B are a cross-sectional side view and a top view, respectively, of a dummy gate 120 and dielectric capping layer 130 arranged on a substrate 101 (bulk substrate). The substrate 101 includes one or more semiconductor materials. Non-limiting examples of suitable substrate 101 materials include Si (silicon), strained Si, SiC (silicon carbide), Ge (germanium), SiGe (silicon germanium), SiGeC (silicon-germanium-carbon), Si alloys, Ge alloys, III-V materials (e.g., GaAs (gallium arsenide), InAs (indium arsenide), InP (indium phosphide), or aluminum arsenide (AlAs)), II-VI materials (e.g., CaSe (cadmium selenide), CaS (cadmium sulfide), CaTe (cadmium telluride), ZnO (zinc oxide), ZnSe (zinc selenide), ZnS (zinc sulfide), or ZnTe (zinc telluride)), or any combination thereof. In an exemplary embodiment, the substrate 101 includes germanium so that the channel region has both electron and hole mobility properties.

A doped source 103 is arranged on the substrate 101 over a counter-doped layer 102. The doped source 103 and the counter-doped layer 102 are formed on the substrate 101 incorporating dopants into the substrate 101 or forming an epitaxial growth layer on the substrate 101. The doped source 103 is heavily doped with a dopant, which may be a p-type dopant (e.g., boron) or an n-type dopant (e.g., phosphorus or arsenic). The counter-doped layer 102 includes a dopant that is different/opposite the dopant in the doped source 103. For example, when the doped source 103 includes a p-type dopant, the counter-doped layer 102 includes an n-type dopant, and when the doped source 103 includes an n-type dopant, the counter-doped layer 102 includes a p-type dopant. The doped source 103 is heavily doped, including a dopant concentration in a range from about 10¹⁹ to about 10²² atoms/cm³. The thickness of the counter-doped layer 102 may be in a range from about 5 to about 50 nm, or from about 10 to about 20 nm. The thickness of the doped source 103 may be in a range from about 50 to about 250 nm, or from about 100 to about 200 nm.

A dummy gate 120 is disposed on the doped source 103 between a first spacer 110 and a second spacer 111. The first spacer 110 is deposited on the doped source 103, the dummy gate 120 is deposited on the first spacer 110, and the second spacer 111 is deposited on the dummy gate 120.

The first spacer 110 and second spacer 111 may include an insulating material, for example, silicon dioxide, silicon nitride, SiOCN, or SiBCN. Other non-limiting examples of materials for the first spacer 110 and the second spacer 111 include dielectric oxides (e.g., silicon oxide), dielectric nitrides (e.g., silicon nitride), dielectric oxynitrides, or any combination thereof. The first spacer 110 and second spacer 111 materials are deposited by a deposition process, for example, chemical vapor deposition (CVD) or physical vapor deposition (PVD). The first spacer 110 and the second spacer 111 may each have a thickness of about 3 to about 15 nm, or of about 5 to about 10 nm.

The dummy gate 120 includes a sacrificial gate material, for example, amorphous silicon (aSi) or polycrystalline silicon (polysilicon). The sacrificial material may be deposited by a deposition process, including, but not limited to, physical vapor deposition (PVD), chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), inductively coupled plasma chemical vapor deposition (ICP CVD), or any combination thereof. The sacrificial material forming the dummy gate 120 has a thickness of about 8 to about 100, or from about 10 to about 30 nm.

A dielectric capping layer 130 is deposited on the second spacer 111 over the dummy gate 120. Non-limiting examples of materials for the dielectric capping layer 130 include silicon dioxide, tetraethylorthosilicate (TEOS) oxide, high aspect ratio plasma (HARP) oxide, high temperature oxide (HTO), high density plasma (HDP) oxide, oxides (e.g., silicon oxides) formed by an atomic layer deposition (ALD) process, or any combination thereof. The dielectric capping layer 130 has a thickness in a range from about 30 to about 200 nm, or from about 50 to about 100 nm.

FIGS. 2A and 2B are a cross-sectional side view and a top view, respectively, after forming a trench 201 through the dielectric capping layer 130, second spacer 111, and the dummy gate 120 to expose the first spacer 110. The trench 201 extends from a surface of the dielectric capping layer 130 to the first spacer 110, exposing the first spacer 110. The trench 201 is formed by performing an etch process that is selective to (will not substantially remove) the first spacer 110 material. The etch process may be, for example, a reactive ion etch. Multiple etching processes are performed to form an opening/trench within the structure. For example, a first etching process is performed to remove a portion of the dielectric capping layer 130 selective to the material of the second spacer 111. A second etching process is then performed to remove a portion of the second spacer 111, which underlies the portion of the trench 201 formed from the first etching process, selective to the material of the dummy gate 120. A third etching process is then performed to remove a portion of the dummy gate 120, which underlies the portion of the trench 201 formed from the second etching process, selective to the material of the first spacer 110. The resulting trench 201 extends through a top surface of the dielectric capping layer 130 down to a top surface of an exposed portion of the first spacer 110. The width of the trench 201 may be about 3 to about 20 nm, or about 5 to about 10 nm. The depth of the trench 201 may be about 50 to about 300 nm, or from about 100 to about 200 nm.

FIGS. 3A and 3B are a cross-sectional side view and a top view, respectively, after etching through the first spacer 110 to expose the doped source 103 and form a self-aligned junction. The first spacer 110 may etched using a process that is selective to (will not substantially remove) the doped source 103 material. The first spacer 110 may be etched by, for example, a reactive ion etch (RIE). The exposed portion of the first spacer 110 is removed by an etching process to expose a portion of the underlying source contact layer. This creates a self-aligned junction because a source extension can be epitaxially grown from the source layer to a top surface of the first spacer layer.

FIGS. 4A and 4B are a cross-sectional side view and a top view, respectively, after oxidizing a portion of the dummy gate 120 sidewall. A thin layer of oxide 401 is formed along the sidewall. The oxidation may be performed by a plasma oxidation process or other oxidation process that forms a thin oxide 401 layer. A portion of the first spacer 110 or the doped source 103 also may be oxidized. Any oxide formed in these regions is removed before performing the epitaxial growth (see FIGS. 5A and 5B).

FIGS. 5A and 5B are a cross-sectional side view and a top view, respectively, after growing an epitaxial layer on the doped source 103 to form the epitaxial channel 501 (channel region). The channel 501 extends vertically from the source and through the trench 201 extending through the dummy gate 120, first spacer 110, and second spacer 111. The epitaxial growth includes an epitaxial semiconductor material, and the epitaxial growth and/or deposition processes are selective to forming on semiconductor surface and do not deposit material on other surfaces, such as the oxide 401, first spacer 110 or second spacer 111. The epitaxial growth in the epitaxial channel 501 extends over the dielectric capping layer 130.

The epitaxial channel 501 may be grown using a suitable growth process, for example, chemical vapor deposition (CVD), liquid phase (LP) or reduced pressure chemical vapor deposition (RPCVD), vapor-phase epitaxy (VPE), molecular-beam epitaxy (MBE), liquid-phase epitaxy (LPE), metal organic chemical vapor deposition (MOCVD), or other suitable processes.

The sources for the epitaxial channel 501 material may be, for example, silicon, germanium, or a combination thereof. The gas source for the deposition of epitaxial semiconductor material may include a silicon-containing gas source, a germanium-containing gas source, or a combination thereof. For example, an epitaxial silicon layer may be deposited from a silicon gas source that is selected from the group consisting of silane, disilane, trisilane, tetrasilane, hexachlorodisilane, tetrachlorosilane, dichlorosilane, trichlorosilane, methylsilane, dimethylsilane, ethylsilane, methyldisilane, dimethyldisilane, hexamethyldisilane and combinations thereof. An epitaxial germanium layer can be deposited from a germanium gas source that is selected from the group consisting of germane, digermane, halogermane, dichlorogermane, trichlorogermane, tetrachlorogermane and combinations thereof. An epitaxial silicon germanium alloy layer can be formed utilizing a combination of such gas sources. Carrier gases like hydrogen, nitrogen, helium and argon can be used.

FIGS. 6A and 6B are a cross-sectional side view and a top view, respectively, after planarizing the epitaxial growth in the epitaxial channel 501. The planarization process may be a CMP process. Planarization removes excess epitaxial growth over the dielectric capping layer 130.

FIGS. 7A and 7B are a cross-sectional side view and a top view, respectively, after partially recessing the epitaxial channel 501, filling with a dielectric material 701, and planarizing the dielectric material 701. The epitaxial channel 501 is partially recessed to a level that is still within the dielectric capping layer 130 and over the second spacer 111. The epitaxial channel 501 is recessed by etching, for example, by a reactive ion etch or a wet etch process.

The recessed formed over the recessed epitaxial channel 501 is filled with a dielectric material to form a dielectric cap on a distal end of the channel 501 and over the second spacer 111. The dielectric material 701 may be a dielectric oxide (e.g., silicon oxide), a dielectric nitride (e.g., silicon nitride), a dielectric oxynitride, or any combination thereof. The dielectric material 701 is deposited by a deposition process, for example, chemical vapor deposition (CVD) or physical vapor deposition (PVD). After deposition, the dielectric material 701 is planarized, by for example, CMP.

FIGS. 8A and 8B are a cross-sectional side view and a top view, respectively, after removing the dielectric capping layer 130 and forming an epitaxial growth 801 on a distal end of the epitaxial channel 501 to form a drain over the dummy gate 120 and second spacer 111. The epitaxial growth 801 of the drain is arranged between the dielectric material 701 and the epitaxial channel 501. The epitaxial growth 801 is also arranged between the dielectric cap and the dummy gate 120. A portion of the epitaxial channel 501 over the second spacer 111 may be recessed along sidewalls before forming the epitaxial growth 801. The epitaxial growth 801 forms the drain. In other embodiments, the epitaxial growth 801 forms the source. The epitaxial growth may be performed as described above in FIGS. 5A and 5B.

FIGS. 9A and 9B are a cross-sectional side view and a top view, respectively, after depositing a spacer 901 on the epitaxial growth 801. The spacer 901 protects the epitaxial growth 801 of the drain. The spacer 901 is also disposed on a sidewall of the dielectric material 701. The spacers 901 extend around the drain from the second spacer 111 to a surface of the dielectric material 701. The spacer 901 includes an insulating material, for example, dielectric oxides (e.g., silicon oxide), dielectric nitrides (e.g., silicon nitride), dielectric oxynitrides, or any combination thereof. The spacer 901 material is deposited by a deposition process, for example, chemical vapor deposition (CVD) or physical vapor deposition (PVD). The spacer material may be etched by a dry etch process, for example, a RIE process, such that it covers the epitaxial growth 801 and is removed from a surface of the dielectric material 701 and the second spacer 111. The spacer 901 has a width 902 (thickness) of about 5 to about 50 nm, or from about 15 to about 30 nm.

FIGS. 10A and 10B are a cross-sectional side view and a top view, respectively, after removing a portion of the second spacer 111 and dummy gate 120. The second spacer 111 and the dummy gate material 120 are recessed to removed portions that extend horizontally beyond the spacer 901 material. An etch process that is selective to (will not substantially remove) the first spacer 110 is performed. The etch process may be a dry etch process, such as a RIE process.

FIGS. 11A and 11B are a cross-sectional side view and a top view, respectively, after removing the remaining dummy gate 120 material beneath the spacer 901 to expose the oxide 401. The dummy gate 120 material may be removed by a wet etch process, for example, a process that includes hot ammonia.

FIGS. 12A and 12B are a cross-sectional side view and a top view, respectively, after removing the dummy gate oxide 401 layer and depositing a gate dielectric material 1201 and a work function metal 1202. The dielectric material 1201 and the work function metal 1202 form a portion of the gate stack that replaces the dummy gate 120. The gate dielectric material 1201 and the work function metal 1202 are disposed on the first spacer 110, the epitaxial channel 501, the spacer 901, and remaining portions of the second spacer 111 beneath the epitaxial growth 801.

The gate dielectric material(s) can be a dielectric material having a dielectric constant greater than 3.9, 7.0, or 10.0. Non-limiting examples of suitable materials for the gate dielectric material 1201 include oxides, nitrides, oxynitrides, silicates (e.g., metal silicates), aluminates, titanates, nitrides, or any combination thereof. Examples of high-k materials (with a dielectric constant greater than 7.0) include, but are not limited to, metal oxides such as hafnium oxide, hafnium silicon oxide, hafnium silicon oxynitride, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide, zirconium silicon oxide, zirconium silicon oxynitride, tantalum oxide, titanium oxide, barium strontium titanium oxide, barium titanium oxide, strontium titanium oxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, and lead zinc niobate. The high-k material may further include dopants such as, for example, lanthanum and aluminum. The gate dielectric material 1201 layer may be formed by suitable deposition processes, for example, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), evaporation, physical vapor deposition (PVD), chemical solution deposition, or other like processes. The thickness of the gate dielectric material 1201 may vary depending on the deposition process as well as the composition and number of high-k dielectric materials used.

The work function metal(s) 1202 may be disposed over the gate dielectric material 1201. The type of work function metal(s) 1202 depends on the type of transistor. Non-limiting examples of suitable work function metals 1202 include p-type work function metal materials and n-type work function metal materials. P-type work function materials include compositions such as ruthenium, palladium, platinum, cobalt, nickel, and conductive metal oxides, or any combination thereof. N-type metal materials include compositions such as hafnium, zirconium, titanium, tantalum, aluminum, metal carbides (e.g., hafnium carbide, zirconium carbide, titanium carbide, and aluminum carbide), aluminides, or any combination thereof. The work function metal(s) 1202 may be deposited by a suitable deposition process, for example, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, and sputtering.

FIGS. 13A and 13B are a cross-sectional side view and a top view, respectively, after filling with a metal gate material 1401 and planarizing the metal gate material 1401. The metal gate material 1401 is a conductive gate metal that is deposited over the gate dielectric material(s) 1201 and work function metals 1202 to form the gate stack. Non-limiting examples of suitable conductive metals include aluminum (Al), platinum (Pt), gold (Au), tungsten (W), titanium (Ti), or any combination thereof. The conductive metal may be deposited by a suitable deposition process, for example, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, and sputtering. A planarization process, for example, chemical mechanical planarization (CMP), is performed to polish the surface of the conductive gate metal material 1401.

FIGS. 14A and 14B are a cross-sectional side view and a top view, respectively, after partially recessing the metal gate material 1401. The metal gate material 1401 is partially recessed by an etch process, for example, a RIE process.

FIGS. 15A and 15B are a cross-sectional side view and a top view, respectively, after etching the gate dielectric material 1201 and the work function metal 1202. An anisotropic etch is performed such to recess the gate dielectric material 1201 and the work function metal 1202 down to the level of the metal gate material 1401. The anisotropic etch may be a RIE process.

FIGS. 16A and 16B are a cross-sectional side view and a top view, respectively, after performing gate lithography and etching to form the gate 1601. A mask may be disposed on the metal gate material 1401 and subsequently patterned. The pattern is transferred into the metal gate material 1401 to remove a portion of the metal gate material 1401 and define the gate 1601. In addition, the gate dielectric material 1201 and work function metal 1202 are also etched during this step. A combination of RIE processes may be performed. A portion of the first spacer 110 is arranged between the gate stack of the gate 1601 and the doped source 103. The gate 1601 replaces the dummy gate 120 and is arranged in contact with the channel 501.

FIGS. 17A and 17B are a cross-sectional side view and a top view, respectively, after depositing a liner layer 1720 on the gate 1601 and the spacers 901 around the epitaxial growth 801 forming the drain. The liner layer 1720 is arranged in contact with the gate 1601. The liner layer 1720 may include any material(s) that will remain substantially intact when the spacers 901 and dielectric material 701 are etched, as described below. The liner layer 1720 may include a material that is different than the spacers 901 and dielectric material 701.

The liner layer 1720 may include an insulating material. The liner layer 1720 is arranged on sidewalls of the spacers 901. Non-limiting examples of insulating materials for the liner layer 1720 include dielectric nitrides (e.g., silicon nitride), dielectric oxides (e.g., silicon oxide), dielectric oxynitrides, or any combination thereof. The liner layer 1720 may be formed using a suitable deposition process, including, but not limited to CVD, PVD, plasma enhanced CVD, atomic layer deposition (ALD), evaporation, chemical solution deposition, or like processes. The liner layer 1720 may have a thickness in a range from about 2 to about 50 nm, or from about 5 to about 10 nm.

FIGS. 18A and 18B are a cross-sectional side view and a top view, respectively, after depositing an inter-layer dielectric (ILD) 1830 on the liner layer 1720 and planarizing. The ILD 1830 may be formed from, for example, a low-k dielectric material (with k<4.0), including but not limited to, silicon oxide, spin-on-glass, a flowable oxide, a high density plasma oxide, borophosphosilicate glass (BPSG), or any combination thereof. The ILD 1830 is deposited by a deposition process, including, but not limited to CVD, PVD, plasma enhanced CVD, atomic layer deposition (ALD), evaporation, chemical solution deposition, or like processes.

FIGS. 19A and 19B are a cross-sectional side view and a top view, respectively, after forming source contacts 1940 over the doped source 103. It is noted that the source contacts 1940 are only shown in FIG. 19B, and not in FIG. 19A, because the source contacts 1940 are arranged at an end of the gate 1601. The source contacts 1940 extend through the ILD 1830 and first spacer 110 to the doped source 103 and are formed within a trench. To remove the ILD 1830 and form the source trenches, a resist, such as a photoresist, may be deposited and patterned. An etch process, such as a RIE, may be performed using the patterned resist as an etch mask to remove the ILD 1830 and first spacer 110 until the doped source 103 is exposed. The source trenches are filled with a conductive material or a combination of conductive materials. The conductive material filling may be a conductive metal, for example, aluminum (Al), platinum (Pt), gold (Au), tungsten (W), titanium (Ti), or any combination thereof. The conductive material may be deposited by a suitable deposition process, for example, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, or sputtering. A planarization process, for example, CMP, is performed to remove any conductive material from the surface of the ILD 1830.

FIGS. 20A and 20B are a cross-sectional side view and a top view, respectively, after forming gate contacts 2050. The gate contacts 2050 extend from the surface of the ILD 1830, through the liner layer 1720, and to the gate 1601. The gate contacts 2050 are formed by patterning a trench in the ILD 1830 and liner layer 1720. The trench extends from a surface of the ILD 1830 and through the liner layer 1720 to the gate 1601. To remove the ILD 1830 and form the gate contact trenches, a resist, such as a photoresist, may be deposited and patterned. An etch process, such as a RIE, may be performed using the patterned resist as an etch mask to remove the ILD 1701 until the gate 1601 is exposed. The gate contact trenches are filled with a conductive material or a combination of conductive materials. The conductive material may be a conductive metal, for example, aluminum (Al), platinum (Pt), gold (Au), tungsten (W), titanium (Ti), or any combination thereof. The conductive material may be deposited by a suitable deposition process, for example, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, or sputtering. A planarization process, for example, CMP, is performed to remove any conductive material from the surface of the ILD 1830.

FIGS. 21A and 21B are a cross-sectional side view and a top view, respectively, after removing the dielectric material 701 and spacers 901 surrounding the epitaxial growth 801 forming the drain. The liner layer 1720 surrounding the drain allows for selective etch removal of the spacers 901 and dielectric material 701 over and around the drain to expose the epitaxial growth 801. A hollow opening (open cavity) surrounding the drain within the liner layer 1720 is formed. One or more wet and/or dry etch processes may be used to selectively etch around the drain, leaving the liner layer 1720 and ILD 1830 substantially intact. Examples of suitable etch processes include etch chemistries using, for example, HF or HCl, or tetramethylammonium hydroxide (TMAH).

FIGS. 22A and 22B are a cross-sectional side view and a top view, respectively, after depositing a metal 2260 on the drain to form drain contacts. The metal 2260 is deposited within the hollow opening within the liner layer 1720. The drain contact surrounds the epitaxial growth 801 forming the drain and extends from the second spacer 111 over the drain. The metal 2260 forming the drain contact contacts the drain on a surface (upper/top surface) and a sidewall. The drain contact is wider than the drain itself. The drain all-around contact (top electrode contact) resistance is reduced compared to a drain contact that only contacts a single surface of the drain. Non-limiting examples of metals for the metal 2260 include aluminum (Al), platinum (Pt), gold (Au), tungsten (W), titanium (Ti), or any combination thereof. The metal 2260 may be deposited by a suitable deposition process, for example, CVD, PECVD, PVD, plating, thermal or e-beam evaporation, or sputtering. A planarization process, for example, CMP, is performed to remove any conductive material from the surface of the ILD 1830.

The descriptions of the various embodiments of the present invention have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The terminology used herein was chosen to best explain the principles of the embodiments, the practical application or technical improvement over technologies found in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein. 

What is claimed is:
 1. A vertical transistor, comprising: a source layer arranged on a substrate; a channel extending vertically from the source layer; a drain arranged on a distal end of the channel that opposes the source layer, the drain comprising an epitaxial growth; and a drain contact comprising a metal wrapped around all exposed areas of the drain, the metal being disposed on and around the drain such that the metal contacts all exposed sidewalls of the drain; and a liner layer disposed directly on sidewalls of the metal of the drain contact, the liner layer comprising an insulating material.
 2. The vertical transistor of claim 1, further comprising a gate surrounding and in contact with the channel, wherein the liner layer is also disposed on the gate.
 3. The vertical transistor of claim 2, further comprising a gate contact extending from a surface of an ILD and through the liner layer to the gate.
 4. The vertical transistor of claim 1, wherein the liner layer has a thickness in a range from about 2 to about 50 nm.
 5. The vertical transistor of claim 1, wherein the liner layer is a dielectric nitride, a dielectric oxide, a dielectric oxynitride, or a combination thereof. 